fix: few UBs; fix: missing error handler for malloc

This commit fixes some few UBs (Undefined Behaviors) based on numerous sanitizers, and also adds the missing error handling for a "malloc" call.

zygiskd/src/companion.c

@@ -54,6 +54,7 @@ void *entry_thread(void *arg) {
   pthread_exit(NULL);
 }
 
+/* WARNING: Dynamic memory based */
 void entry(int fd) {
   LOGI("New companion entry.\n - Client fd: %d\n", fd);
 

zygiskd/src/root_impl/kernelsu.c

@@ -9,7 +9,11 @@
 
 #include "kernelsu.h"
 
-#define KERNEL_SU_OPTION 0xdeadbeef
+/* INFO: It would be presumed it is a unsigned int,
+           so we need to cast it to signed int to
+           avoid any potential UB.
+*/
+#define KERNEL_SU_OPTION (signed int)0xdeadbeef
 
 #define CMD_GET_VERSION 2
 #define CMD_UID_GRANTED_ROOT 12

zygiskd/src/zygiskd.c

@@ -360,6 +360,7 @@ struct __attribute__((__packed__)) MsgHead {
   char data[0];
 };
 
+/* WARNING: Dynamic memory based */
 void zygiskd_start(char *restrict argv[]) {
   LOGI("Welcome to ReZygisk %s Zygiskd!\n", ZKSU_VERSION);